Search

Portable power supplies, particularly lithium‐ion batteries (LIBs), will play a key role in achieving sustainable development goals, and electrode active materials for the next generation of LIBs with higher energy density and longer life time is highly demanded. For this, in situ visualization of Li behavior during the charge/discharge process is essential, and transmission electron microscopy (TEM) will be promising for this purpose. Here, a quite simple experimental setup consisting of a newly developed Li–C nanocomposite film sputter‐deposited onto Au nanoprotrusions at room temperature and graphene synthesized on a W probe at 500 °C for the in situ TEM observation of the battery reaction is proposed. The preservation of the metallic Li in the Li–C film that is transferred to TEM without using any transfer vessels under atmospheric conditions is confirmed by high resolution TEM before the in situ electrochemical process in TEM. After the one cycle of the in situ electrochemical process, the intercalation of Li ions into graphene (lithiation) is clearly observed. Thus, it is concluded that the metallic Li stored in the Li–C film works well as the anode active material in the electrochemical process for solid state LIBs, implying the developed in situ experimental system is promising. [ABSTRACT FROM AUTHOR]

We report the field emission characteristics of a few-layer pristine and N-doped graphene by the in-situ transmission electron microscopy. The measurements were performed with a Pt-Ir nanoprobe and at a vacuum gap of 400 nm. The turn on voltage, required to draw an emission current of 1 nA from pristine and N-doped graphene, was found to be 230 and 110 V, respectively. The lower turn on voltage for the N-doped graphene can be explained from the improved electrical conductivity and up-shift of the Fermi level with nitrogen doping. Structural deformation/contraction/buckling of the N-doped graphene sheet was observed with the field emission current exceeding ∼6.9 μA, which can be attributed to the Joule heating. [ABSTRACT FROM AUTHOR]

This study demonstrates graphitization directly through the amorphous carbon under the catalysis of a low‐melting‐point metal, gallium (Ga), by heating in a vacuum heater as well as by Joule heating during in situ transmission electron microscopy (TEM) operation. For the material system of the mixture of Ga nanoparticles (NPs) and amorphous carbon matrix, the graphitization temperature is determined to be about 600 °C for the first time. With increasing the temperature, evaporation and agglomeration of small Ga NPs start to occur together with the graphitization at around the places where Ga NPs would have been located at the surface region. In situ TEM experiment reveals the accelerated increase in electrical conductivity with structural change from amorphous to graphitization. Thus, the combination of the in situ and ex situ TEM observations is believed to be a lead step to understand deeper the graphitization process and provide information in nanoscale. [ABSTRACT FROM AUTHOR]

Graphene synthesis at lower temperatures is quite important for a wider range of practical applications. Sn, which is recently found as a promising catalyst for the low-temperature graphene growth, is taken as the study material in this work. Based on the detailed transmission electron microscopy (TEM) observation, we found that catalytic activity of Sn nano-particles is highly temperature dependent which was observed during graphitization of amorphous carbon. For this study, C–Sn composite nanofibers were prepared on an edge of a carbon foil by the Ar+ ion irradiation with simultaneous supply of Sn. As-fabricated C–Sn composite nanofibers were observed to be the amorphous C nanofibers (CNFs) in which the Sn nanoparticles dispersed. The as-prepared samples were annealed at 180–250 °C in a vacuum and were characterized using Raman spectra and high-resolution TEM to study the graphitization process. The graphitization started to occur at an annealing temperature of 180 °C, which is much lower than the graphitization temperature for bulky Sn. Based on the detailed TEM observation of annealed samples, a model to explain the graphitization mechanism at such a low temperature was proposed. [ABSTRACT FROM AUTHOR]

A development of the technique that enables the simple, rapid, and damage‐free sample preparation for cross‐sectional transmission electron microscopy (X‐TEM) analyses is quite important. Here, we propose a silicon (Si) oxide nanofiber (SON) formed on a tip of an atomic force microscope cantilever as a substrate onto which materials in question are deposited for X‐TEM analyses. Based on the technique for the ion‐irradiation–induced carbon nanofiber (CNF) fabrication onto atomic force microscope cantilever tips, Si‐included CNFs (Si‐CNFs) were fabricated onto cantilever tips. The prepared Si‐CNFs were then annealed at 1000°C in atmospheric ambient to form SON‐tipped cantilevers. Si oxide nanofiber, consisting of mostly Si and O, was linear in shape and was amorphous in crystalline structure. The high performance of the SON‐tipped cantilever was demonstrated for the X‐TEM analyses of ZnO films deposited thereon by an arc plasma deposition method, suggesting that it is promising as a substrate for X‐TEM analyses. [ABSTRACT FROM AUTHOR]

A graphite foil was irradiated with argon (Ar+) ions to fabricate conical structures with a carbon nanofiber (CNF) on top of the structure. The field emission (FE) properties of one-dimensional individual CNF-tipped cones that had been fabricated were carefully measured by in situ transmission electron microscopy (TEM) facilities. The highest FE current, 550 nA, was observed in the current-voltage (I-V) measurement of a single CNF. Almost no degradation in I-V properties were detected during the reliability test after 30 min. TEM images indicated that the CNF was amorphous in nature initially, and that the electron current flow in the FE process induced the dramatic change in the crystalline structure of both the CNF and of the tip region of the basal cone part. After performing the FE process, the crystalline structures of the amorphous CNFs were transformed into ring-shaped graphene layers, whereas nanodiamond like nanoparticles formed in the outer layer of the tip region of the basal cone. The structural changes induced can be attributed to Joule heating under the high electric field. [ABSTRACT FROM AUTHOR]

Small-scale batch fabrication of Co-included carbon nanofibers (Co-CNFs) onto commercially available Si cantilevers for scanning probe microscope by an Ar+-ion-irradiation method with a simultaneous Co supply was demonstrated (eight chips/batch). As confirmed by scanning and transmission electron microscopes equipped with energy dispersive x-ray spectroscopy, Co-CNFs were fibrous and contained Co and C. With increasing the Co supply rate, Co-CNFs decreased in length from ∼600 to ∼400 nm, whereas their diameter was almost independent of the Co supply rate, 20–30 nm. As proven by magnetic force microscope (MFM) measurements using the Co-CNF probes, they were applicable as MFM probes. Since various metals including alloys can be incorporated into CNFs, this ion-irradiation method with a simultaneous metal supply was believed to be quite promising for the functionalization of CNF probes for a variety of applications. [ABSTRACT FROM AUTHOR]

Abstract: A very simple method to synthesize densely distributed carbon nanofibers (CNFs) on flexible plastic substrates at room temperature with no catalyst is demonstrated. Carbon film was deposited onto polyimide, poly-ethylene-terephthalate (PET) films, Si plates and a Ni mesh, which were then sputtered with obliquely incident Ar+ ions at 3keV at room temperature. Linear-shaped CNFs oriented in the incidence direction of the ion beam grew on the sputtered substrates, as confirmed by scanning (SEM) and transmission electron microscopes (TEM). CNF growth on a PET substrate, which is a non-heat-tolerant plastic, has never been reported so far. CNFs thus grown were characterized as amorphous without a hollow structure. The diameter of CNFs was almost identical (20–30nm) despite a large difference in CNF length (0.1–4μm). In addition, the CNF-tipped cones were demonstrated to act successfully as a template to fabricate one dimensional (1-D) zinc oxide (ZnO) nanostructures on a PET substrate. Thus, it was believed that the ion-irradiation technique would open up a new approach to fabricate any kinds of 1-D nanomaterials on flexible substrates at room temperature. [Copyright &y& Elsevier]

ZnO nanobamboos and nanowires with diameters of 10–30 nm and lengths of 2–4 μm have been prepared by laser ablation in vacuum with precisely controlled pressure, growth and post-annealing temperature. XRD results show the annealed sample is hexagonal ZnO. Low-magnified TEM observation reveals the annealed sample includes ZnO nanobamboos and nanowires. High resolution TEM image and electron diffraction pattern confirm that the structure of ZnO nanobamboo is regular stacking of Zn and O layers with high crystal quality. The growth direction is determined as along [001] direction (c axis). TEM observations confirm that the formation of bamboo-shape ZnO is due to the stacking fault and cleavage. The bundle of those stacking faults seems to be the origin of the black contrast at the nodes. The uniformity of chemical composition for the nanobamboos is identified by EDS profiles. A strong-narrow UV band centred at 390 nm and a weak-broad green band centred at 515 nm are observed at room temperature in the PL spectrum recorded from the annealed ZnO nanobamboos and nanowires. [ABSTRACT FROM AUTHOR]

Metallic lithium (Li) anode batteries have attracted considerable attention due to their high energy density value. However, metallic Li is highly reactive and flammable, which makes Li anode batteries difficult to develop. In this work, for the first time, we report the synthesis of metallic Li-embedded carbon nanocomposites for easy and safe handling by a scalable ion beam-based method. We found that vertically standing conical Li-C nanocomposite (Li-C NC), sometimes with a nanofiber on top, can be grown on a graphite foil commonly used for the anodes of lithium-ion batteries. Metallic Li embedded inside the carbon matrix was found to be highly stable under ambient conditions, making transmission electron microscopy (TEM) characterization possible without any sophisticated inert gas-based sample fabrication apparatus. The developed ion beam-based fabrication technique was also extendable to the synthesis of stable Li-C NC films under ambient conditions. In fact, no significant loss of crystallinity or change in morphology of the Li-C film was observed when subjected to heating at 300 °C for 10 min. Thus, these ion-induced Li-C nanocomposites are concluded to be interesting as electrode materials for future Li-air batteries. [ABSTRACT FROM AUTHOR]

In this work, we utilize Joule heating to convert Pt-embedded amorphous carbon nanofiber (CNF) to multiwall carbon nanotube (CNT) in a transmission electron microscope (TEM). The transformation process of Pt-embedded amorphous CNF to multiwall CNT and nano-soldering process using Pt encapsulated CNT was investigated in TEM in detail. Molten Pt-encapsulated inside CNF and CNT always flowed towards the anode, proving electromigration to be the dominant force over thermal migration. Controllable electromigration of Pt was utilized to connect the Pt-included CNT to another CNT, thus forming a seamlessly welded CNT structure. Further, two separate CNF were brought together to form Y-contact which was transformed into Y-junction CNT structure by controlled electromigration of Pt. Changes in morphology and electrical property during CNT formation and nano-soldering were probed in real time with high resolution TEM. Our method provides a procedure for the position control synthesis of CNT and its nano-soldering which can be an important step for future development of a CNT based nanoelectrical circuit. [ABSTRACT FROM AUTHOR]

The cross-sectional transmission electron microscopy for the Li-C nanocomposite film deposited on Au-nanoprotrusions (AuNPs) revealed the instantaneous formation of solid electrolyte interphase (SEI) at the initial stage of cyclic voltammetry measurement. [Display omitted] • One-step and room temperature process to spontaneously generate a dense array of Au- nanoprotrusions (AuNPs) was demonstrated. • The AuNPs were promising as a platform for cross-sectional transmission electron microscopy (X-TEM) analyses. • Because of the easy tunability of the composition of AuNPs, they are promising also as a platform for materials design. Au-nanoprotrusions (AuNPs) were fabricated on a gold substrate using obliquely incident Ar+ ions with a simultaneous supply of carbon at room temperature. The sputter erosion rate was kept almost constant at 49 nm/min, while the deposition rate of carbon ranged from 1.2 to 0.6 nm/min. Scanning electron microscopy (SEM) observation revealed the variation in the number density and shape of the AuNPs ranging from slender needles to cones with a large apex angle, depending on the carbon deposition rate. Transmission electron microscopy (TEM) demonstrated that the slender needles were characterized by the bi-metal like structure of the large Au grain-rich phase and amorphous carbon phase with a dispersion of fine Au nanoparticles, while the conical structures consisted of Au grains with an amorphous carbon cap region on top. Those structures were selectively prepared, depending on the application. Li-C nanocomposite films deposited on conical structures, for instance, were readily observed cross-sectionally by TEM without any post treatment, revealing the instantaneous formation of a solid electrolyte interphase (SEI) after only 2 charge-discharge cycles in the cyclic voltammetry (CV) measurement. Thus, AuNPs are promising as a platform for the materials design and characterization in atomic dimensions. [ABSTRACT FROM AUTHOR]

Doping of a foreign element in sp 2 hybridized graphene lattice is of significant importance to tune the electrical and chemical properties. Here, we report on the grain structures of substitutional nitrogen-doped graphene synthesized by an atmospheric pressure (AP) solid source-based chemical vapor deposition (CVD) technique. Nitrogen-doped graphene was synthesized by mixing solid camphor and melamine as carbon and nitrogen source, respectively. The precursor materials quantity significantly affects the graphene growth on Cu foil and thereby the nitrogen doping and content. Transmission electron microscopy (TEM) analysis was performed to determine the nitrogen substitutional sites in the graphene. Dark-field (DF) TEM analysis was carried out to evaluate the graphene grain structure grown with introduction of nitrogen dopant. We obtained different grain orientations, where an individual grain size is more than 5 μm. Our findings show that graphitic nitrogen defects can be introduced in the large individual graphene grain by the developed solid source-based CVD technique. [ABSTRACT FROM AUTHOR]

Abstract: We present a direct observation of structural change in Au-incorporated carbon nanofiber (CNF) during a field emission (FE) process using an in situ transmission electron microscopy (TEM). The TEM images and their electron diffraction pattern together with electron energy loss spectroscopy (EELS) indicated that the amorphous carbon structure of CNF was transformed to hollow graphitic structure catalyzed by dispersed Au particles before FE. Thus, the in situ TEM study will be promising to reveal the formation process of nanocarbon materials by solid phase reaction depending on the catalyst metal element for metal-incorporated CNFs. [Copyright &y& Elsevier]